Periodontal diseases are infectious diseases which range from simple gingival inflammation to rapidly progressive diseases resulting in loss of the bony support of the teeth. About ten percent of adult Americans, some 30 million individuals, are at high risk for severe periodontal disease and resultant tooth loss. Since this tooth loss occurs because of the destruction of bone tissue the National Institute of Dental Research strategic plan "Broadening the Scope:long-Range Research Plan for the Nineties" has recommended that periodontal researchers "elucidate the mechanisms of tissue destruction in periodontal diseases adapting advances in molecular biology...... to understand these mechanisms" The ultimate effector cell in periodontal bone loss is the osteoclast. It possesses a highly specialized proton generating mechanism for the rapid dissolution of bone mineral, and secretes collagenases, cathepsins and other hydrolases active in the degradation of bone matrix proteins. Its function, as well as its formation from hemopoietic precursors, is stimulated by immune cell mediators which are abundant in the inflammatory periodontal lesion. It is therefore important to understand osteoclast ontogeny and function in order to more fully comprehend mechanisms associated with bone loss in periodontal disease and to design successful strategies for intervention. Thus, we have undertaken to gain a fuller understanding of these mechanisms by adapting advances in molecular biology in order to dissect the mRNA phenotype of the osteoclast. In so doing, our objective is to identify and characterize molecular probes which are specific to cells of the osteoclast lineage, as well as those which reflect the efferent and afferent mechanisms which regulate and define its function as the cell responsible for the bone loss associated with periodontal disease. We shall utilize cDNA libraries that we have constructed from highly purified preparations of rabbit osteoclasts. We propose to screen these libraries using strategies designed to identify clones which may serve as osteoclast-specific markers for the study of osteoclast ontogeny, as well as to select for functionally relevant genes which are specifically regulated when osteoclast resorption is activated. Clones identified by these screens will be characterized by sequence analysis. Osteoclast-specific clones will be examined by in situ hybridization for temporal and spatial patterns of expression during osteoclast formation in fetal limbs. Clones for osteoclast genes which are functionally regulated will be studied using gene-specific antisense oligodeoxynucleotides to determine whether inhibition of their translation effects the ability of osteoclasts to function in in vitro assays of resorption and attachment. Finally, in order to detect rarely expressed genes in these libraries, we propose to conduct large scale sequencing of 3000 clones to obtain important new information to databases on the molecular phenotype of the osteoclast.